1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having an electron gun capable of improving a resolution of an image by preventing electron beams from striking electrodes and efficiently controlling a spot size that is susceptible to a change in current capacity.
2. Background of the Related Art
FIG. 1 is an explanatory view of a general cathode ray tube in a related art.
As depicted in FIG. 1, the cathode ray tube consists of a panel 1 with a fluorescent screen 13 formed on its inner surface, in which R, G, and B fluorescent substances (or phosphors) are applied to the screen, a funnel 12 fused to a rear end of the panel 10 for maintaining the inside of the tube in a vacuum state, an electron gun housed inside of a neck portion 15 of the funnel 12 for emitting electron beams, a deflection yoke 11 for deflecting the electron beams emitted from the electron gun 16, and a shadow mask 14 with a color selecting function for the electron beams that are deflected by the deflection yoke 11.
Normally in this kind of cathode ray tube, the electron beams emitted from the electron gun 16 are deflected by the deflection yoke 11 in the horizontal and vertical directions, and then pass through the shadow mask 14, and eventually strike the fluorescent screen 13.
When that happens, each fluorescent substance (i.e. R, G and B) applied to the fluorescent screen 13 is radiated or emits light, thereby creating a desired image.
FIG. 2 diagrammatically illustrates the structure of an electron gun according to a related art.
Referring to FIG. 2, the electron gun consists of a cathode 20 working as an electron beam generator, a first electrode (G1) 21 and a second electrode (G2) 22 whose potential difference constitutes, in combination with the cathode 20, a pre-focus lens, a third electrode (G3) 23 and a fourth electrode (G4) 24 and a fifth electrode (G5) 25 that constitute a pre-main lens for converging electron beams, and a fifth electrode 25 and a sixth electrode (G6) 26 that constitute, in combination with the pre-main lens, a main lens for converging the electron beams onto the fluorescent screen.
Besides the above, there is one more main component of the electron gun, i.e. a shield cup 27, which is fused to the sixth electrode 26 in order to shun off the outside electric field and magnetic field. The electrodes are then fused and fixed to a bead glass 28.
Particularly, the fourth electrode 24, as illustrated in FIG. 3, is a plate electrode having a predetermined thickness, t. Also, formed on the fourth electrode are three circular electron beam passing holes 24b which are spaced out by a predetermined distance from each other for passing through R, G and B electron beams.
Further, projection type bead supports 24a are disposed at the top and bottom sides of the fourth electrode 24. Mainly, the bead supports 24a are used to make sure that the electrodes are securely fused and fixed to the bead glass 28.
FIG. 4(a) is a plan view of the second electrode 22 for the conventional electron gun, explaining the structure of the second electrode 22, and FIG. 4(b) is an enlarged cross-sectional view of a part xe2x80x9c22exe2x80x9d in FIG. 4(a).
As depicted in the drawing, the second electrode 22 basically looks similar to the above-discussed fourth electrode 24. That is, the second electrode 22 is a plate electrode like the fourth electrode 24, and it has three circular electron beam passing holes 22b disposed at regular intervals for passing through R, G and B electron beams, and bead supports 22a for ensuring electrodes to be securely fused and fixed to the bead glass 28.
As for the second electrode 22, however, each electron beam passing hole 22b is surrounded by an outer concentric circle, namely, a coining part 22b, which serves to minimize manufacturing difficulties and deformation, and formed inside the coining part 22d is a rectangular shaped recess 22c with a constant, unified depth in the horizontal direction at an opening part of the second electrode 22 towards the third electrode 23.
More specifically, the recess 22c forms a groove having a constant depth, and the electron beam passing hole 22b is located at the center of the groove. In fact, one can more easily fabricate the electron beam passing hole 22b by having the electron beam passing hole 22b be formed in the recess 22c with a relatively thinner thickness than the total thickness of the second electrode 22.
Now turning to the operation of the electron gun with the above structure, first of all, an electron beam is formed by the first electrode 21 and the second electrode 22, and the electron beam is primarily converged by the pre-focus lens formed by the potential difference between the second electrode 22 and the third electrode 23, and then largely converged by the pre-main lens formed by the potential difference among the third electrode 23, the fourth electrode 24, and the fifth electrode 25.
The electron beam having been primarily converged by the pre-main lens passes the main lens formed by the potential difference between the fifth electrode 25 and the sixth electrode 26, and is again converged and accelerated, thereby forming an electron beam spot on the fluorescent screen.
The third electrode 23 and the fifth electrode 25 have the unified potential, which is, in general, between 6000V and 10000V.
In addition, the second electrode 22 and the fourth electrode 24 have the unified potential, which is, in general, between 300V and 1000V.
Each in-line type electron beam in opposition to the R, G and B fluorescent substances applied to the fluorescent screen 13 is converged to one single point so as to reproduce a desired color.
In other words, those three electron beams are respectively converged by the main lens, and combined to a focal point on the fluorescent screen 13, forming an electron beam spot on the screen.
In connection with convergence of the spot on the screen, Japanese Patent Publication No. 53-18866 discloses a method for preventing deterioration in the convergence of spots on the screen by forming a recess 22c in the horizontal direction at the opening part of the second electrode 22 toward the third electrode side 23.
FIG. 5 diagrammatically depicts the shape of an electron beam incidented upon the main lens and the shapes of electron beams exhibited on the fluorescent screen.
Referring to FIG. 5, the electron beam incidented upon the main lens is horizontally oblong, that is, the width (a) is longer than the length (b). It is so because the depth toward the direction of the electrode thickness of the recess 22c is large. In result, the electron beam is very astigmatic, and deflection aberration observed on the entire screen can be well compensated.
As such, the ratio of the length to the width, b/a, and size of the electron beam incidented on the main lens contributes to the spot size throughout the screen and further resolution of a cathode ray tube. As shown in FIG. 6, the ratio of the length to the width, b/a, of the electron beam incidented on the main lens is closely connected to the depth, d, of the recess formed on the second electrode 22 and the vertical width (size), W, of the recess.
There have been numbers of attempts to reduce the deflection aberration of electron beams and deterioration of beam spot in the vicinity of the screen by, for example, forming the recess 22c on the second electrode 22 and making the ratio of the depth, d, to the width, W, of the recess 22c (d/W) greater than 0.3 so as to generate severely astigmatic beams, and then adjusting the ratio of d to W of the electron beam incidented on the main lens.
However, the above attempts only gave rise to a problem that the spot size at the center of the screen was vertically elongated due to the astigmatism.
In another aspect, as more and more people are now watching moving images on a computer monitor thanks to a great achievement in Internet development, an electron gun with high brightness for computer monitors was introduced because the monitor cathode ray tube failed to provide substantially realistic and bright pictures as TV cathode ray tube did.
But this kind of electron gun consumed more than three times greater current than the conventional electron gun. The worse part was that the spots throughout the screen got bigger when current consumption was increased, and the resolution was also degraded due to the big spots.
In short, despite the formation of the recess on the second electrode for controlling electron beams, the resolution of the screen was still low in case more current was applied to the electron gun.
Moreover, increase in the current capacity increased the diameter of electron beams as shown FIG. 7 (Dxe2x80x2 greater than D), and this caused the electron beams to strike electrodes, consequently destroying a circuit therein.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Accordingly, one object of the present invention is to solve the foregoing problems by providing a cathode ray tube equipped with an electron gun capable of improving a resolution of an image by preventing electron beams from striking electrodes and efficiently controlling a spot size that is susceptible to a change in current capacity.
The foregoing object and advantages are realized by providing a cathode ray tube equipped with an electron gun consisting of a cathode for emitting electron beams; and a first electrode, a second electrode, a third electrode, a fourth electrode, a fifth electrode, a sixth electrode and a shield cup, which are arranged in the cited order from the cathode to the direction of a (fluorescent) screen, where a vertical size, W, of a recess formed on the second electrode, a depth, d, of the recess, a diameter, A, of an electron beam passing hole formed on the fourth electrode, and a thickness, t, of the electron beam passing hole satisfy a relation of   0.22  ≤            d      W        +          t      A        ≤      0.38    .  
Another aspect of the invention provides a cathode ray tube equipped with an electron gun consisting of a cathode for emitting electron beams; and a first electrode, a second electrode, a third electrode, a fourth electrode, a fifth electrode, a sixth electrode and a shield cup, which are arranged in the cited order from the cathode to the direction of a (fluorescent) screen, coining parts being formed on a front surface of the second electrode at regular intervals, where a thickness, h, of the electrodes without adding a depth of the coining part, a space, s, between the second electrode and the third electrode, a thickness, t, of the fourth electrode, which is spaced out for a predetermined distance from the third electrode, and a diameter, A, of an electron beam passing hole formed on the fourth electrode satisfy a relation of   0.6  ≤            h      s        +          t      A        ≤      0.8    .  
Still another aspect of the invention provides a cathode ray tube equipped with an electron gun consisting of a cathode for emitting electron beams; and a first electrode, a second electrode, a third electrode, a fourth electrode, a fifth electrode, a sixth electrode and a shield cup, which are arranged in the cited order from the cathode to the direction of a (fluorescent) screen, coining parts and recesses being formed on a front surface of the second electrode at regular intervals, where a thickness, h, of the electrodes without adding a depth of the coining part, a vertical size, W, of the recess, a depth, d, of the recess, a space, s, between the second electrode and the third electrode, a thickness, t, of the fourth electrode, which is spaced out for a predetermined distance from the third electrode, and a diameter, A, of an electron beam passing hole formed on the fourth electrode satisfy relations of   0.22  ≤            d      W        +          t      A        ≤      0.38    ⁢          xe2x80x83        ⁢    and    ⁢          xe2x80x83        ⁢    0.6    ≤            h      s        +          t      A        ≤      0.8    .  
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.